Regenerative direct current motor braking control



Ncv. 17, 1970 A. w. wlLKERsoN REGENERATIVE DIRECT CURRENT MOTOR BRAKING CONTROL Original Filed 0G11.' 2l, 1965 5 Sheets-Sheet 1 INVENTOR WILKERSON ATTORNEYS Nov. 17, 1970 A. w. wlLKERsON 3,541,414

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Nov. 17, 1970 REGENERATIVE DIRECT CURRENT MOTOR BRAKING CONTROL original Filed oct. 21, 1965 Invnm'on ALAN w. wILKERsoN BY $01001 TRM,

A'r'roRNnYs Nov. 17, 1970 A. w. wlLKERsoN l 3,541,414

REGENERATIVE DIRECT CURRENT MOTOR BRAKING CONTROL Original Filed Oct. 21, 1965 v 5 Sheets-Sheet 4 INVENTOR ALAN W. HILKBRSON BY MAW ATTORNEYS 5 Sheets-Sheet 5 INVENTOR WILKERSON ATTORNEYS ALAN w. m i

"ill- QQN Nov. 17, 1970 A. w. wlLKl-:RsoN

REGENERATIVE DIRECT CURRENT MOTOR BRAKING CONTROL Original Filed Oct. 2l, 1965 Sie n IIIIIII |||||||L %\N VIN y &\\ L NL QNKV United States Patent O1 hee 3,541,414 Patented Nov. 17, 1970 3,541,414 REGENERATIVE DIRECT CURRENT MOTOR BRAKING CONTROL Alan W. Wilkerson, Thensville, Wis., assignor, by mesne assignments, to Web Press Engineering, Inc., Addison, Ill., a corporation of Illinois Original application Oct. 21, 1965, Ser. No. 499,409, now Patent No. 3,435,316, dated Mar. 25, 1969. Divided and this application Oct. 16, 1968, Ser. No. 767,983

Int. Cl. H02p 5/06, 7/06 U.S. Cl. 318-302 8 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCES TO RELATED APPLICATIONS This application is a divisional application of copending application Ser. No. 499,409, field Oct. 2l, 1965, now issued as U.S. Pat. 3,435,316 on Mar. 25, 1969.

FIELD OF THE INVENTION The present invention relates to electrical motive power systems and more particularly to those providing regenerative braking to a direct current motor.

DESCRIPTION oF THE PRIOR ART `DC motor braking-General Many applications of DC motors require that the motor be braked during operation. For example, extremely accurate speed control may require that the motor be braked as soon as it exceeds a desired speed. Other examples include DC motors subjected to overhauling loads, as in crane, hoist, and elevator service.

The method and apparatus for controlling such braking action have presented problems for many years. A simple mechanical brake on the motor output shaft is sometimes employed. While such a device is inexpensive, its braking action is difficult to control. Maintenance of the mechanical brake also raises problems. The use of an external electro-mechanical brake, such as an eddy current brake, solves some of the foregoing problems but, on the whole, external brakes have generally proven unsatisfactory.

A DC motor may also be braked by adjusting the ener gization of the armature and field of the motor. One such method is termed plugging and involves reversing the motor armature voltage and current when it is desired to brake the motor. While the reduction in speed is rapid and the electrical apparatus required is little and inexpensive, the high circulating currents in the armature circuit place a large thermal strain on the motor. Repeated braking operations cannot be performed without excessive heating and damage to the motor.

In dynamic braking of a DC motor, a resistor is placed in the armature circuit. The motor in effect becomes a DC generator supplying power to the resistor load. While a resistor limits the armature current and hence the thermal strain on the motor, it also decreases the effectiveness of the braking action, particularly at low speeds.

Regenerative braking of DC motors also employs the motor as a generator, similar to dynamic braking. However, the vital difference is that in regenerative braking the power generated by the motor is supplied back to the active power source for the motorrather than being circulated through a passive resistor load. Reduced to its essence, power may be regenerated, or supplied back to the active power source for the motor, by reversing the polarity of the armature voltage while maintaining armature current flow in the same direction or by reversing armature current flow while maintaining the polarity of the armature voltage. In'either case the motor that was formerly a load becomes a power source. The advantages of such a system include the fact that braking may be done on a permanent basis, whereas plugging and dynamic braking are effective only in transient conditions or for isolated stops. Also, with proper control, the arm-y ature current may be limited, thereby eliminating the excessive motor heating experienced with other methods of braking. Braking may also be accomplished very rapidly.

Although alternating current is used as input power to a direct current motor control for many reasons, its use is particularly adapted to DC motor controls providing regenerative braking to the motor. As the voltage polarity of such an input is continually reversing on a periodic basis, voltage of either polarity may be supplied to the motor by connecting the alternating current source to the motor at the proper time.

During motoring operation, the DC motor control recties the alternating current input to use half cycles of one polarity of the AC power to apply a'unipolarity voltage to the motor armature. The motor field is also energized with direct current to cause the motor to rotate. The rotation of the armature through the flux of the motor generates a counter opposing the applied voltage. The power control means, such as controlled rectifers, in the control are arranged to be properly biased for conduction any time the counter is more negative than the applied Voltage and to supply power from the control as a source to the motor as a load.

During regenerative operation, to cause'the motor to become a source for the control, the direction of the motory field `winding current flow is reversed, reversing the motor flux and the polarity of the counter (assuming the direction of motor rotation remains instantaneously the' same). The reversed counter again biases the controlled rectifiers to conduct current, in the same direction as during motoring, any time the counter E.M.F..'is

more negative than the applied alternating voltage. This.:

includes portions of the half cycles of the other polarity,

this permitting the reversal of voltage at the control ter- .i minals necessary for regenerative operation. A regenera. tive DC motor control must therefore provide unidirec tional current in the armature circuit any time the counter of the motor is more negative thanthe alternatingV voltage of the alternating current power source. This're-I. quires control during all of one half of each -zcycle of."

the alternating current input and for a portion.of the other half cycle of that input.

Prior art static, regenerative direct current motor controls have often been hampered in their operation by` faulty operation of the field circuit used to energize the` motor field winding. As noted above, the field circuit of the control must reverse the direction of currentow through the motor field winding in order for the motor to operate regeneratively. In the past, most regenerative motor controls have dissipated the inductive energy of the motor field winding, generated as the winding is deenergized in one current flow direction and re-energized in the other, into a resistive network. This dissipation requires some finite time interval and during this time interval the motor is in neither the motoring state nor the 3 regenerative state, but is essentially uncontrolled. Because of the uncontrolled state of the motor during this time interval, the accurate speed regulation desired of a regenerative motor control is substantially lessened.

Further, the field circuits of prior art controls providing the bi-directional current fiow to the motor field winding have generally been prone to electrical malfunctions which create excessive current in the field circuit. This actuates fuses or other safety devices, disabling the motor field and the control. Such electrical malfunction may occur when the field circuit accidentally provides current in both directions through the motor field winding at the same time. Such malfunction is often caused by the stray firing of a controlled rectifier in the field circuit by electrical noise or other spurious signals existing in the field circuit. Under such conditions, no current passes through the motor field winding, but a dangerously high current circulates in the field circuit. The resulting disabling of the field circuit shuts down the control, regardless of vwhether the source of the spurious signals continues to be present, reducing the utility of the control.

SUMMARY OF THE INVENTION The present invention provides a regenerative, direct current motor control which provides for regenerative operation of the motor by reversing the direction of current iiow through the motor field winding, often herein termed simply reversing the motor field. Further, the control provides for a rapid reduction and reversal of the motor field winding current, thereby limiting the time interval during which the control loses regulation over the condition of the motor. Such rapid reduction of the motor field winding current is accomplished by regeneratingthe inductive energy of the motor field Winding back to the motor field power supply.

The field circuit of the control includes controlled rectifier means for controlling the direction of current fiow through the motor field winding from an alternating current input, said circuit being constructed so that stray firing of the controlled rectifiers does not damage the control or the motor. The maximum effect that such an occurrence may have is an alteration of the operation of the control for one half cycle of the alternating current input.

The firing circuit of the motor field circuit used to control the controlled rectifier means operates around zero input signals to control two groups of complementary controlled rectifiers in the means. The firing circuit does not drift off zero in response to temperature changes or changes in other operating conditions and has no input hysteresis.

The present invention provides in combination, a static, regenerative direct current motor control -which obtains regeneration of power from a motor operatively associated with the control to a power supply by reversing the motor field current; and a motor field circuit means for energizing the motor field winding and for reversing the direction of current fiow through the motor field winding. The field circuit means includes a controlled rectifier means connected to an alternating current power supply for providing either direction of current fiow through the motor field winding from the power supply. A firing circuit is provided for controlling the controlled rectifier means in accordance with a bi-condition input signal to the control. The firing circuit has means for providing first firing pulses during the half cycles of the alternating current power supply, the provision of these pulses being dependent on the presence and condition of the input signal. These pulses are used to control the controlled rectifier means so as to provide current fiow through the motor field -winding in the desired direction. The firing circuit also has means for providing second firing pulses to the controlled rectifier means during each half cycle. The provision of these firing pulses is independent of the input signal and occurs in the latter portion of each half 4 cycle. These pulses are used to control the controlled rectifier means to discharge the inductive energy of the motor field winding back to the power supply to'rapidly reduce the field current to zero.

The present invention also provides, in combination, the static regenerative direct current motor control and a motor field circuit means including two DC sources having their outputs connected in parallel with the field winding for providing current fiow in either direction through the motor field winding responsive to a control signal from the control to the circuit means. The field circuit means includes current limiting impedances inserted in the outputs of the DC sources. The DC sources may be energized from an alternating current power supply and include a controlled rectifier means for providing half waves of rectified alternating current to the motor field so that in the event both of the DC sources simultaneously supply power to the motor field, such conditions may exist for only one half cycle of alternating current and the impedances limit the current through the DC sources to prevent damage thereto.

BRIEF DESCRIPTION OF THE DRAWING The specification includes the following drawings, forming a part thereof:

FIG. 1 is a schematic diagram of the static, regenerative direct current motor control-field circuit combination of the present invention;

FIG. 2 is a graph of an alternating current wave form showing the principles of motoring and regenerative operation of the control;

FIG. 3 is a detailed schematic drawing of an operational amplifier which may be used in the control of FIG. 1;

FIG. 4 is a schematic diagram of a controlled rectifier firing circuit which may be used to operate the controlled rectifier means in the motor field circuit of the control of FIG. 1;

FIG. 5 is a schematic diagram of a controlled rectifier firing circuit which may be used to operate the rectifiers of the controlled rectifier bridge in the armature circuit of the control shown in FIG. 1;

FIG. 6 is a schematic diagram of a current regulating and regenerative logic circuit which may be used in the control shown in FIG. 1; and

FIG. 7a and b are wave forms illustrating the regenerative operation of the motor field.

DESCRIPTION OF PREFERRED EMBODIMENT Brief description of regenerative direct current motor braking control a block diagram of a regenerative, DC motor control 10- constructed in accordance with the present invention is shown therein. Control 10 includes reference and feedd back circuit 14, operational amplifier 16, field circuit 18, and armature circuit 20. The control drives the DC motor 22 consisting of armature 24 and motor field 26, each of which includes or comprises an electromagnetic coil or Winding. The control is provided with input power from three phase AC lines 28.

Reference and feedback circuit 14 includes a reference signal source 30 providing a variable DC signal to conductor 32 by means of DC supply 33 and potentiometer 31. A feedback signal is provided by tachometer 34 which is connected to armature 24 and supplies a -DC signal corresponding to the speed of armature 24 to conductor 36. Conductors 32 and 36 are joined at mixing junction 38 which provides an error signal to conductor 40. This error signal may be of either polarity and serves as a motoring control signal in one polarity and a regenerative braking control signal in the other polarity.

The error signal in conductor 40 is fed to operational amplifier 16 which provides a high degree of amplification to the error signal. In subsequent portions of the specification or in the claims, this amplifier may be termed the first amplifier to distinguish it from other amplifiers in control 10. Amplifier 16 has two output signals, both of which have abrupt saturation points. Both of the signals are proportional in magnitude to the input signal. However, the polarity of one output signal is the same as the polarity of the input error signal in conductor 40 (termed the direct output signal) while the other output signal is of the opposite polarity from the input error signal in conductor 40 (termed the inverse output signal). The graph of these output signals forms an X with the direct output signal forming one stroke, and the inverse output `signal forming the other and the two signals meeting at zero output for operational amplifier 16. One of the output signals is used to control both field circuit 18 and armature circuit 20 While the other is used to control only armature circuit 20. While FIG. 1 shows the inverse output signal of operational amplifier 16 as .being supplied to both field circuit 18 and armature circuit 20 and the direct output signal of operational amplifier 16 as supplied through conductor 239 to armature circuit 20 only, the connection of these output signa-ls may be reversed and the invention is not to be interpreted as limited to the connection shown in FIG. l. In any event, both signals are employed throughout all operational sequences of control 10.

Field circuit 18 includes motor field 26. The field circuit is supplied with alternating current from AC `supply lines 28 through transformer 42. The output of transformer 42 contains a controlled rectifier means comprising two groups of oppositely connected controlled rectifiers 44 and 46 and 48 and 50. These rectifiers control the direction of current fiow through the winding of motor field 26, one group of rectifiers being energized for each direction of current flow. A field controlled rectifier firing circuit 52, which may be considered a pushpull proportional firing circuit, controls the operation of controlled rectifiers 44 through 50 in response to the inverse output signal from operational amplifier 16. The control provided by field control-led rectifier yfiring circuit S2 determines which group of controlled rectifiers will be placed in the conductive state and may also include a determination of the magnitude of the field current. Firing circuit 52 also provides for rapid reversal of the current through motor field 26 by controlling the operation of the controlled rectifiers in a manner to regenerate the motor field current back to AC supply lines 28.

Field circuit 18 also contains a resistive network cornprising resistors 54 and 56. These resistors act as a limiting impedance to prevent short circuits in the motor field power circuit in the event of faulty firing of the controlled rectifiers and, as a secondary function, reduce the time constant of motor field 26. Resistors 58 and 71 provide a means of sensing the polarity of the motor field current.

Armature circuit 20 supplies power to armature 24 during motoring operation and receives power from armature -24 during regenerative operation. Armature circuit 20 is supplied with power during motoring operation from AC supply lines 28 through transformer 60. The amount of power provided to armature 24 is controlled by armature controlled rectifier bridge 62 containing controlled rectifiers 146 through 151. Terminals 306 and 307 constitute the output terminals of control 10. During regenerative operation power is supplied from motor armature 24 through armature controlled rectifier bridge 62 and transformer 60 back to AC supply -lines 28.

Armature controlled rectifier firing circuit 64 controls the operation of the rectifiers in armature controlled rectifier bridge 62. In order to provide reverse voltage capabilities, this firing-circuit must be capable of controlling the operation of the controlled rectifiers through one entire half cycle of alternating current from supply Vlines 28 and through a portion of the other half cycle.

The current regulating and regenerative logic circuit 66 performs a dual function. The regenerative logic portion thereof determines whether a combination of conditions in control are proper for regenerating or motoring operation and operates armature circuit 20 accordingly. In making such determination, the logic circuit utilizes a pair of AND gates operable by a field polarity signal supplied by sensing resistors 58 and 71 through conductors 68 and 69 as well as the direct and inverse output signals from operational amplifier 16 supplied through conductors 238 and 239. The current regulating portion of circuit 66 regulates the armature current during motoring or regenerative operation and utilizes an armature current feedback signal supplied by conductor 70.

Description of operation of regenerative direct current motor braking control The operation of control 19 may be better understood by initial reference to FIG. 2 in which the numeral 228 indicates the alternating voltage supplied to the control through AC supply lines 28. The supply voltage 228 includes a positive half cycle 229 and a negative half cycle 230. Only a single phase of alternating current is shown in FIG. 2 to simplify the explanation.

As previously mentioned, armature 24 generates a counter while rotating in the motoring state. This counter is indicated in FIG. 2 by the graph 224 for the motoring operation of control 10. The controlled rectifiers 146, 148, and in armature rectifier bridge 62 may conduct any time applied voltage 228 is more positive than counter 224 since, as shown in FIG. 1, the anodes of the controlled rectifiers may be considered connected to AC supply voltage 228 while the cathodes of the rectifiers are connected to the armature and counter 224. The controlled rectifiers are properly biased for conduction anytime the anodes are more positive than the cathodes. This is the time interval between T1 and T2. The amount of power supplied to armature 24 and the speed of the motor 22 during motoring operation is determined by the point between T1 and T2 at which the rectifiers of rectifier bridge 62 are rendered conductive. The closer to time T1 the rectifiers are rendered conductive, the greater the supplied power.

During regenerative operation, the energization of motor field 26 is reversed, reversing the polarity of the counter of the motor. The reversed counter is shown by the graph 225 in FIG. 2. It will be noted that the time during which the counter E.M.F. of the motor is more negative than the applied voltage is now much greater, extending from time T5 to Time T4. Referring to negative half cycle 230 it will also be noted that time T3 to time T4 the voltage on the anodes of the controlled rectifiers 146, 148, and 150` in bridge 62, that is, applied alternating voltage 228 has negative polarity with reference to the AC source.

Since the anodes of the controlled rectifiers are more positive than the cathodes thereof, even though they are negative with reference to the AC source, the controlled rectifiers can conduct current in the same direction through bridge 62 if a signal is provided from armature controlled rectifier firing circuit 64. This current will flow from armature 24 through the controlled rectifiers of armature bridge 62 and through transformer 60` in regenerative fashion to AC supply lines 28. This is due to the fact that the polarity of the voltage on bridge 62 has reversed while the direction of current flow therethrough remains the same.

It is evident from the foregoing that armature controlled rectifier firing circuit 64 must be capable of firing the controlled rectifiers both from time T1 to time T2, for motoring operation, i.e., when the counter E.M.F. is more negative than the applied AC voltage, and also between time T3 and T4 for regenerative operation, i.e., when the applied AC voltage has reversed its polarity but before it becomes more negative than the counter E.M.F.

The operation of control in the manner shown graphically in FIG. 2 is accomplished by employing two operational loops. These may be termed the inner loop and the outer loop to indicate that the former operates within the confines of the latter. The outer operational loop is utilized to control motor speed and comprises tachometer 34, operational amplifier 16, current regulating and regenerative logic circuit 66, armature controlled rectifier firing circuit 64, armature controlled rectifier bridge 62 and armature 24. The outer loop controls the operation of control 10 as long as operational amplifier 16 is unsaturated. When operational amplifier 16 saturates, the above described outer loop becomes inoperative since further error signal changes in conductor 40 are not transmitted through operational amplifier 16. For normal speed regulating operation, however, the operational amplifier of the outer loop is not saturated and the inner loop serves as an active part of the outer loop.

The inner operational loop is used to regulate armature current at all times in accordance with the amplified error signal from amplifier 16. It comprises the armature current feedback signal in conductor 70, current regulating and regenerative logic circuit 66, armature controlled rectifier firing circuit 64, armature controlled rectifier bridge 62, and armature 24. The inner loop is a complete feedback regulator employing as a reference signal one of the outputs of amplifier 16, as selected by the logic portion of current regulating and regenerative logic circuit 66, and as feedback, the signal in conductor 70. The gain and response of this inner loop regulator are sufficient to cause the armature current to accurately and rapidly follow the signal from amplifier 16, thereby causing the magnitude of armature current to be proportional to the error signal in conductor 40. However, when the error signal becomes large enough to saturate the outputs of amplifier 16, further increases in error signal can no longer cause an increase in armature current, since the reference signal to the inner current loop regulator cannot be larger than the saturated output of amplifier 16. In this manner the maximum armature current is sharply limited to a value corresponding to the saturated output of amplifier 16. One other consideration is important. Since the output of amplifier 16 may change almost instantly from a low level to its highest value the nature of response of the inner loop current regulator to an instantaneous rise in reference signal must include a complete lack of overshoot to prevent transient currents from being larger than the desired maximum value.

The field circuit 18 is operated open loop at or below the base speed of DC motor 22 except for the field polarity signal in conductors 68 and 69 to current regulating and regenerative logic circuit 66. Above the base speed of DC motor 22, field weakening is required.

To operate control 10, switch 72 is closed to energize the circuitry of the control. Reference signal source 30 is .adjusted to provide a signal corresponding to desired speed. The signal is supplied through conductor 32 to junction 38 and thence to operational amplifier 16. Operational amplifier 16 produces a direct output signal and an inverse output signal proportional to the input signal in conductor 40. As armature 24 is not yet rotating there will be no feedback signal supplied by tachometer 34.

Field circuit 18 utilizes one of the output signals from operational amplifier 16 to turn on either rectifiers 44 and 46 or rectifiers 48 and 50 by means of field controlled rectifier firing circuit 52. The desired direction of rotation of the motor is determined by which of the two groups of controlled rectifiers is turned on.

Both the inverse output signal and the direct output signal of operational amplifier 16 are supplied to Current regulating and regenerative logic circuit 66. This circuit determines whether conditions in control 10 are proper for motoring or regenerative operation by means of the polarity of the output signals of operational amplifier 16 and the motor field polarity signals in conductors 68 and 69. These signals operate the pair of AND gates in the logic portion of current regulating and regenerative logic circuit 66 and operate the armature circuit accordingly. For the present motoring operation, the logic portion of current regulating and regenerative logic circuit 66 determines that control 10 is, in fact, capable of such operation and passes the amplified error signal to the inner current regulating loop and thence to armature controlled rectifier firing circuit 64. Armature controlled rectifier firing circuit 64 provides a firing signal to the controlled rectifiers of armature controlled rectifier bridge 62 to energize armature 24 and accelerate the armature.

Acceleration of the armature 24 causes tachometer 34 to generate a feedback signal in conductor 36 which reduces the magnitude of the error signal in condustor 40. This likewise reduces the magnitude of both outputs of operational amplifier 16 and causes armature controlled rectifier firing circuit 64 to retard the firing angle of the controlled rectifiers in armature controlled rectifier bridge 62. Regulation of the speed of armature 24 is obtained by controlling the point of firing of the controlled rectifiers in armature controlled rectifier bridge 62 between time T1 and time T2, as shown in FIG. 2, by the combined operation of the inner and outer operational loops.

Regenerative operation of control 10 may be brought on by reducing the reference signal in conductor 32 or by providing an overhauling load to armature 24. In either case, the feedback signal generated by tachometer 34 in conductor 36 exceeds the reference signal generated by reference signal source 30 in conductor 32. This reverses the polarity of the error signal in conductor 40 and hence the polarity of the inverse output signal and direct output signal from operational amplifier 16. Because of the high gain of operational amplifier 16 a small reversal in the polarity of the error signal is sufficient to initiate regenerative operation.

The reversed polarity of the output signal from operational amplifier 16 to field controlled rectifier firing circuit 52 causes the latter circuit to energize the other group of controlled rectifiers in field circuit 18 reversing the current through motor field 26. The time of reversal is short because the inductive energy stored in the winding of motor field 26 is regenerated through transformer 42 to AC supply lines 28 and because resistors 54 and 56 reduce the time constant of the field. The reversal of motor field 26 reverses the counter of armature 24 and the polarity of the signal in conductors 68 and 69.

Operational amplifier 16 provides output signals of reversed polarity to the regenerative logic portion of current regulating and regenerative logic circuit 66. In the absence of the correct motor field polarity signal from conductors 68 and 69 the logic circuit produces no output at all. The correct signal in conductor -68 or 69, indicating motor field has completed reversal, provides a signal from current regulating and regenerative logic circuit `66 to armature controlled rectifier firing circuit 64 which controls the point of firing of the controlled rectifiers between time T3 and T4 as shown in FIG. 2 depending on the magnitude of the error signal in conductor 40. As described in connection with that figure this operation provides regenerative power to alternating current supply lines 28.

If the error signal in conductor 40 is excessively large during either motoring or regeneration, the operational amplifier 16 becomes saturated and control over armature circuit conditions is delegated to the inner loop including current regulating portion of current regulating and regenerative logic circuit 66. The current feedback. signal is supplied from the armature circuit to the current regulating portion of current regulating and regenerative logic circuit 66. This circuit alters the output signal to armature controlled rectifier firing circuit 64, after comparing the feedback signal with a reference signal comprised of the saturated output of operational amplifier 16, to retard a firing angle of the controlled rectifiers in armature controlled rectifier bridge 62 to maintain the armature current at the desired maximum value.

The following comprises the detailed description of the various components of control shown in FIG. 1. It iS to be understood that the invention is not limited to the specific embodiments incorporated in this detailed description but may utilize equivalent circuits having similar functional characteristics.

DETAILED DESCRIPTION OF OPERATIONAL AMPLIFIER As previously mentioned, this amplifier has a single input and two outputs. Both of the output signals are proportional in magnitude to the input signal. However, the polarity of one output signal is the same as the polarity of the input signal while the other output signal is opposite in polarity to the input signal. The first mentioned output signal has been termed the direct output signal while the latter signal is termed the inverse output signal. The amplifier must, of course, be capable of handling input signals from conductor 40 of either polarity.

FIG. 3 shows a circuit suitable for use as operational amplifier 16 of control 10. The operational amplifier contains two complementary, three-stage amplifiers. One such amplifier, 73, is formed of transistors 74, 76 and 78 while the other such amplifier, 75, is formed from transistors 80, 82 and 84. The input transistors of each of the aforementioned amplifiers, that is, transistor 74, and transistor 80 are closely matched for identical characteristics, so that the tendency of one such transistor to drift under operating conditions will be closely matched by the same tendency of the other transistor, thereby producing equality in the overall effect on the two amplifiers.

Amplifiers 73 and 75 are powered by a power supply consisting of transformers 86, diodes 88, and 89 and capacitors 90 and 91. The power supply also includes a voltage divider consisting of resistor 92 and resistor 93.

For reasons of overall circuit operation, it is desirable to maintain the input to input transistors 74 and 80 at zero volts. Thus, a low impedance path for the small base current required to establish the operating points of transistors 74 and 80 is provided by resistors 94 and 95 lwhich are joined to the center of the voltage divider network. The voltage divider network provides a smallivoltage `which is used to null the small voltage drop across resistors 94 and 95 caused by the current.

The input signal from conductor 40 is applied to operational amplifier 16 at terminals 96 and 97. A pair of diodes 98 and 99 connected in opposite polarities across input terminals 96 and 97 limit the magnitude of the input signals to that which can be handled by the operation of the amplifier. Specifically, when the magnitude of the input signal exceeds the forward conduction voltage of diodes 98 or 99, the diodes break down and short circuit terminals 96 and 97 thereby preventing an input signal in excess of the breakdown voltage from reaching amplifiers 73 or 75. This prevents excessive input signals from overdriving either of the amplifiers. Two diodes 98 and 99 are provided to accommodate input signals of either polarity.

The amplifier utilizes two feedback circuits, The first of these feedback circuits may be called the common mode feedback as it affects both transistor amplifier 73 and transistor amplifier 75 in an equal manner. The common mode feedback utilizes resistor 100 which measures the sum of the currents through the output of transistors 78 and 84, that is, through the collector and emitter terminals of those transistors. The feedback signal comprising the voltage developed across resistor is compared with a reference signal generated by a voltage di- Nider consisting of resistor 101 and a rheostat 102. The error signal between the feedback signal from resistor 100 and the reference signal from rheostat 102 is supplied through transistor 103 and resistors 104 and 105 to the emitters of transistors 74 and 80 to adjust the sum of the output of these transistors for any difference between the reference signal indicating actual total current. Transistor 75 and resistor 77 establish the operating point of transistor 103. It will be appreciated that a high degree of amplification is obtained through transistor 103 and the three transistors constituting each transistor amplifier 73 and 75 thereby providing rapid, accurate regulation of the sum of the output of transistors 74 and 80.

The second feedback circuit in operational amplifier 16 is termed the differential feedback as it affects differentially amplifiers 73 and 75. This feedback may be resistive, inductive, or capacitive; the character of the feedback changing the operating characteristics of the amplifiers which the feedback serves. For example, varying the resistance of the feedback will vary the amount of gain of the amplifier, while :varying the capacitance of the feedback will vary the response time of the amplifier. Specifically, in FIG. 3 a differential feedback is shown by conductor 106 which provides a feedback signal from the emitter collector circuit of transistor 78 through capacitor 107 to input terminal 97.

The output signals from operational amplifier 16 are supplied to terminals 108 and 109. The direct output signal appears at terminal 108 while the inverse output signal appears at terminal 109.

The first mode of operation, called the common mode, is one in `which a given signal or phenomenon affects both transistor amplifiers 73 and 75 in an equal manner. Examples of common mode signals or phenomenon include variations in line voltage or variations in ambient temperature. As can be readily appreciated, it is necessary that such occurrences affect both transistor amplifier 73 and transistor amplifier 75 equally in order to maintain proper operation of control 10. The second mode of operation, termed the differential mode, is one in which a given signal or phenomenon affects one of the transistor amplifiers in a different manner than it affects the other transistor amplifier. Examples of differential mode signals include an input signal to terminals 96 and 97 or unequal drift of one or the other of transistor amplifiers 73 and 75.

As previously mentioned, the common mode feedback circuit including resistor 100 and the reference circuit including rheostat 102 insure that the total current flowing through output transistors 78 and 84 and transistor amplifiers 73 and 75 is equal to that established by the reference signal. Thus any changes in the total current due to such things as variation in line voltage or in ambient temperature are immediately corrected by the aforementioned reference and feedback signals and the high degree of amplification provided by transistor 103 and the three transistors in each of amplifiers 73 and 7 5.

Operation of operational amplifier 16 in the differential mode to obtain the aforementioned direct output signal and inverse output signal is obtained by first adjusting operational amplifier 16 so that the signals at output terminals 108 and 109 are both equal to zero. Once this is accomplished, variations in the output signal at terminal 109 due to an input signal to terminals 96 and 97, is accompanied by an equal and opposite change in the output signal at terminal 108, as the total current through both transistor amplifiers 73 and 75 must remain the same because of the above described regulation provided by the feedback signal from resistor 100 and the reference signal from rheostat 102.

To provide initial adjustment to operational amplifier 16, output terminal 109 is connected through resistor 81 to input terminal 97. Resistor 81 forms .a negative feedback path which tends to reduce the output signal at terminal 109 of transistor amplifier 73 to zero potential with respect to terminal 96. 'The output signal at terminal 109 is brought to exactly zero by adjusting rheostat 110 to alter the current input to transistor amplifier 75. Assuming that the output signal at terminal 109 is greater than zero, a signal would be applied from rheostat 110 to the input of transistor amplifier 75 to cause that amplifier to conduct more heavily. This removes some of the current flowing through transistor amplifier 73 and reduces the output signal existing at terminal 109. The reduction in current through transistor amplifier 73 occurs because the total current flowing through both transistor amplifiers 73 and 75 must remain at the value regulated by rheostat 102 and hence an increase in the current fiow in one amplifier must require a decrease in current fiow in the other.

After the output signal at terminal 109 has been brought into coincidence with the voltage at input terminals 96 and 97, rheostat 102 is adjusted to alter the output signal at terminal 108 so that it is also at zero. Adjustment of rheostat 102, of course, changes the amount of current inthe output of the two transistor amplifiers 73 and 75. However, since the output of transistor amplier 73 is fixed by the feedback signal between its output terminal 109 and its input terminals 96 and 97, the output of transistor amplifier 75 is varied, thereby to alter the output signal existing at terminal 108. The connection between output terminal 109 and input terminals 96 and 97 may then be removed and from this time on, an input signal to terminals 96 and 97 produces two equal output signals of opposite polarity.

It Will be appreciated that the three stages of amplification in amplifiers 73 and 75 provide a high gain characteristic to operational amplifier 16. This allows the amplifier to be extremely sensitive to changes in the polarity of the error signal in conductor 40 to operate control 10 in the motoring state or the regenerative state as required by that signal. The dead band found in prior art controls of this type, in which the control is unable to operate in the correct state, is thereby eliminated.

As a general rule, the output signal at terminal 109, that is, the inverted output signal is connected to field control rectifier firing circuit 52 and to current regulating and regenerative logic circuit 66. The direct output signal from terminal 108 is also connected to the current regulating and regenerative logic circuit 66. However, it is anticipated that the connections of output terminals 109 and 108 to field control rectifier tiring circuit 52 and to the current regulating and regenerative logic circuit l66 will be reversed in a considerable number of applications of control 10.

DETAILED DESCRIPTION OF MOTOR FIELD CIRCUIT Motor field 26 is energized by center tap transformer 42 which has the motor field 26 connected in the center tap thereof. Each end of center tap transformer has one rectifier of two complementary rectifier groups connected thereto. Specifically, controlled rectifiers 44 and 46 constitute one group of rectifiers and conduct current through motor field 26 in one direction while controlled rectifiers 48 and 50 constitute the other group and conduct current through motor field 26 in the opposite direction. These rectifiers may be, and are shown in FIG. 1 as, silicon controlled rectifiers having an anode terminal, a cathode terminal and a gate terminal. Applying a signal to the gate terminal permits the rectifier to conduct current or fire, when the anode and cathode terminals are properly biased.

IIt will be appreciated that, should one rectifier of each group accidentally be turned on simultaneously, a dead short would result around a circuit comprising the two controlled rectifiers and transformer 42. Such short circuiting has been a failing of prior art controls of this 12 type as it disables the eld circuit. To prevent excessive field current from occurring under such conditions, resistors 54 and 56 are included in the motor field circuit to provide a current limiting impedance. It will be appreciated that if other means are provided to protect the motor field circuit from controlled rectifier misfires, curv rent limiting impedances may be eliminated. These resistors also reduce the inductive time constant of motor field 26 when it is desired to reverse the direction of current fiow through the motor field.

The firing of controlled rectifiers 44 through 50 controlled by field controlled rectifier firing circuit 52 which operates the aforementioned controlled rectifiers to control the amount of current in either direction through the field from zero to maximum and provides for the rapid reversal of the current through motor field 26 by regenerating the inductive energy contained therein back to AC supply line 28. FIG. 4 shows a field controlled rectifier firing circuit which may be used as circuit 52 of control 10 shown in FIG. l. Firing circuit 52 is a pushpull proportional amplifier in that it provides control to one group of rectifiers for an input signal from operational amplifier 16 of one polarity and provides control to the other group of rectifiers for an input signal from operational amplifier 16 of the opposite polarity. IIn instances wherein it is not desired to control the magnitude of the field current, the firing circuit 52 may have sufficient gain so that a small input signal will drive it f-ull Firing circuit 52 contains two unijunction firing circuits 114 and 115, each of which controls one of the groups of controlled rectifiers 44 through 50 in the motor field circuit in response to an input signal supplied to terminals 116 and 117. Each of the unijunction firing circuits includes a unijunction transistor 118 and 119 which provides firing pulses through transistors 120 and 121 to output terminals 122 and 123. For example, output terminal 122 may be connected to controlled rectifiers 44 and 46 while output terminal 123 may be connected to controlled rectifiers 48 and 50. Transistors 120 and 121 insure that the output pulses from unijunction transistors 118 and 119 are of sufficient magnitude and duration to fire controlled rectifiers 44 through 50.

The aforementioned firing circuits 114 and 115 are provided with a main energization circuit, comprised of differential amplifier 124 and alternate energization circuits 125. Differential amplifier 124 is connected to input terminals 116 and 117. A differential amplifier is used to insure an input operating level near zero and to provide balanced push-pull operation. Each of the inputs is connected to a two stage portion of the difierential amplifier 124. Specifically, input 116 is connected to input transistor 126 which in turn is connected to output transistor 127 while input 117 is connected to input transistor 128 and to output transistor 130. IIf the input levels to these terminals is zero, the output from differential amplifier 124 will `be of insufficient magnitude to turn on output transistors 127 and 130. Thus no energizatiton signal will be supplied to unijunction transistors 118 and 119. If input signals in one polarity or the other are supplied to terminals 116 and 117, either transistor 127 or transistor 130 will become conductive. Current flow through the conductive transistor will charge either capacitor 131 or capacitor 132 which will supply an input signal to the respective unijunction transistor 118 or 119, through diodes 300 and 301 to turn on either controlled rectifiers 44 and 46 or controlled rectifiers 48 and 50.

In addition to the aforementioned main energization circuit for unijunction transistors 118 and 119 there is an alternative energization circuit for each of the unijunction transistors which is completely independent of any input signal to terminals 116 and 117. One of these circuits is comprised of resistor 327, resistor 328, and capacitor 329 while the other is comprised of resistor 330, resistor 326 and capacitor 332. The voltage provided by these circuits to the inputs of the unijunction transistors through diodes 133 and 134, respectively, is slightly less than that needed to place the unijunction transistors in the conductive state. The operation of these circuits will be subsequently explained.

- Field controlled rectifier firing circuits 52 is energized from a power supply comprised of transformer 135, diodes 136, 137, and 302 and capacitor 303.

Synchronization of field controlled rectier firing circuit 52 with the alternating current existing in transformer 42 energizing motor field 26 is accomplished by synchronizing circuit 138. synchronizing circuit 138 includes resistor 139, resistor 140, Zener diode 141 and transistor 142. Transistor 142 supplies power across the two base terminals of unijunction transistors 118 and 119 and to alternate energization circuits 125. The period of each half cycle of alternating current input from supply lines 28, during which power will be supplied across the base terminals of unijunction transistors 118 and 119 iS determined by the time interval during which current will fiow through Zener diode 141 and transistor 142. This interval initiates approximately after the beginning of the half cycle and terminates approximately 10 before its end. During this time, a signal supplied from differential amplifier 124 will cause one or the other of unijunction firing circuits 114 and 115 to turn on either one of the two groups of controlled rectifiers 44 through 50 in the motor field circuit 18. The instant at which the firing signal is generated is determined by the magnitude of the input signal to terminal 116 or terminal 117, an input signal of greater magnitude tending to generate a firing signal closer to the initial portions of the half cycle of alternating current, thus controlling the magnitude of the field current as well as its direction.

It is to be noted that since alternating current is applied to the controlled rectifiers, a short circuited condition in the field circuit due to stray firing can exist for only one half cycle AC. At the end of the half cycle, the condition will automatically correct itself as the stray fired rectifier Will be biased nonconductive by the applied AC.

During the time interval that power is supplied to the bases of unijunction transistors 118 and 119, alternate energization circuits 125 will have had sufficient time to charge capacitors 329 and 332 through resistors 327 and 328 and 330 and 326 respectively. However, as previously mentioned, the voltages across capacitors 329 and 332 are insufiicient to fire the unijunction transistors when full input power is applied across the base terminals thereof. Near the end of the cycle, the voltage applied to the base terminals of unijunction transistors 114 and 115 necessarily becomes less as the end of the half cycle of alternating current input approaches. Under these conditions of lessened voltage across the bases of unijunction transistors 118 and 119, the Voltage existing across capacitors 329 and 332 becomes sufiicient to re the unijunction transistors. This generates a firing pulse near the end of each half cycle of alternating current. It is to be noted that the firing signal generated in unijunction transistors 118 and 119 by alternate energization circuits 125 is cornpletely independent of any signal generated in unijunction transistors 118 and 119 by differential amplifier 124, and occurs even though no input is applied to terminals 116 or 117.

With no input signals to terminals 116 or 117, the firing signals caused by alternative energization circuits 125 are supplied to all four rectifiers 44 through 50 of the two complementary groups that control the direction of current fiow through motor field 26. As the firing pulses are supplied to all the rectifiers, the positive voltage generated in two of the rectifiers is opposed by the negative voltage generated in the other two rectifiers so that the net effect of the voltage across the motor field is zero.

When an input signal is applied to terminals 116 and 117, the firing pulse generated by alternative energization source 125 has no effect on the group of rectifiers being controlled by the main energization circuit 124 since one of these rectifiers is already conducting and the other is improperly biased for conduction. The firing pulses provided to the other group of rectifiers by alternative energization source 125 generate a current which opposes the current of the conducting rectifier. However, this condition terminates as the applied voltage reverses and the power loss to motor field 26 is of minor significance as it exists for only 10 of the cycle.

The ring pulses generated by alternate energization circuits 125 are used to rapidly reduce the current of the motor field to zero by regenerating the inductive energy stored in the field back through transformer 42 to AC supply lines 28.

Under normal operation yof motor field circuit 18 where, for example, rectifiers 44 and 46 are alternately rendered conductive Vby field controlled rectifier firing circuit 52, the graph of the voltage at the right hand terminal of the field is shown by the graph 234 in FIG. 7a. This is a fully rectified voltage which produces a DC current 235 through the field. The conducting rectifier is indicated below each half cycle of graph 234.

If, at some time T1, rectifier 46 is not turned on during the appropriate half cycle, current will continue to fioW through the motor field due to its inductive characteristics. In order to maintain this current fiow the motor field 26 becomes a source whose voltage exceeds the applied voltage in transformer 42 during the negative half cycle for rectifier 44. Rectifier 44 will continue to conduct during its normal half cycle as it is then properly biased for conduction. The graph of FIG. 7a subsequent to time T1 shows the field voltage under conditions where rectifier 46 is not turned on. It will be noted that, in effect, alternating voltage is applied to the field. This causes the field current to decay with a slight ripple to zero at time T2. At this time rectier 44 becomes nonconductive as there is no current therethrough and the voltage across the field ceases. It may be noted that the decay of inductive current in the motor field in the above circumstances is no more satisfactory than the time constant of the motor field.

It may also be noted that during the time that the motor field may be considered a source, the field is regenerating power to alternating current lines 28, as current is maintained in the same direction through the circuit but through the polarity of the source terminals in transformer 42, has reversed. However, during the positive half cycle of rectifier 44 power is supplied to the field. This supply and regeneration of power results in little net difference and for all practical purposes may be disregarded. Thus, there is no net regeneration or power supply to the motor field and the inductive energy of the field circuit is dissipated in its resistive portion.

In the control of the present invention, rectifiers 44 and 46 are fired on approximately 10 before the end of the half cycle of applied alternating current voltage by alternate energization means 125 in controlled rectifier firing circuit 52. The effect of this operation is shown in FIG. 7b. As before, a plurality of cycles may be assumed to have preceded the graph in FIG. 7b. Also as before, rectifier 44 is fired on but rectifier 46 is not turned on at the appropriate time to conduct current through the motor field from the AC source. This then causes rectifier 44 to continue to remain on to conduct current from the motor field, as a source, through transformer 42 Approximately 10 before the end of the half cycle rectifier 46 is fired on. This turns off rectifier 44 as the current now has an alternative path through rectifier 46 which is preferred since it is in the direction that transformer 42 desires to provide power to motor field 26. Rectifier 46 conducts power to the motor field for the remaining 10 of half cycle. At the end of the half cycle, the regenerative operation continues as rectifier 44 is not turned on and rectifier 46 is forced to remain on as the only path available for current flow. As

small power supplying portion; the power supplying.

portion being only the final of each half cycle. This rapidly reduces the current in the motor field 26 as shown in FIG. 7b.

DETAILED DESCRIPTION OF ARMATURE CIRCUIT Motor armature 2-4 is inserted across the output terminals of armature controlled rectifier bridge 62 of control 10. Armature controlled rectifier bridge 62 comprises controlled rectifiers 1446, 147, 148, 149, 150, and 151 arranged in complementary pairs and connected in a conventional three phase bridge configuration having output terminals 306 and 307. The three phase secondary winding of transformer 60 is connected to the input terminals of armature controlled rectifier bridge 62,

The control of controlled rectifiers 146 through 151, both as to which rectifiers will conduct and for how long, is controlled by armature controlled rectifier firing circuit 64. As previously mentioned, this firing circuit must control the operation of the controlled rectifiers of armature controlled rectifier bridge 62 throughout the entire period when the counter is more negative than the applied alternating current voltage.

FIG. 5 shows a firing circuit suitable for use as armature controlled rectifier firing circuit 64. Firing circuit 64 is, in reality, three separate firing circuits or amplifiers 264, 364, and 464, each of which is connected to a complementary pair of controlled reetifiers in armature controlled rectifier bridge 62 to conduct current from transformer ,-60 through armature controlled rectifier bridge 62 to armature 24 and back through armature controlled rectifier bridge `62 to transformer 60. The input signal to armature controlled rectifier firing circuit 64 is sup` plied to terminals 156 and 157 and input transistors 158, 159 and 160. These transistors are connected to the three firing amplifiers 264, 364, and 464. Current feedback from the individual firing circuits to input transistors 158 through 160 is provided by resistors 161, 162 and 163, and by rheostat 164 and rheostat 165. These feedbacks stabilize the input to firing circuits 264, 364 and 464 and also, by adjustment of rheostats 164 and 165, balance the inputs of the three individual firing amplitiers.

Firing amplifiers 264, 364 and 464 contain identical circuitry, and for purposes of explanation only firing amplifier 264 will be explained in detail. It is to be understood that firing amplifiers 364 and 464 are identical in construction.

Referring now to firing amplifier 264, the output of input transistor 158 is supplied through resistor 166 to capacitor 167 Which supplies an input to unijunction transistor 168. The output from the base terminals of unijunction transistor 168 is applied to a pair of transistors 169 and 170. These transistors form a two-transistor analogy to a silicon controlled rectifier. That is, they form a four layer semi-conductor structure similar to that found in a silicon controlled rectifier. The combined operation of transistors 169 and 170 is similar to that of a silicon controlled rectifier and it is to be understood that such a controlled rectifier may be used if desired. The two-transistor analogy to silicon controlled rectifier operation is explained more thoroughly in the second edition of the Silicon Controlled Rectifier Manual published by the General Electric Company in 1961.

Certain advantages accrue from the use of two-transistors 169 and 170 rather than a single silicon controlled rectifier in firing amplifier 264. Specifically, the 4firing current and the holding current may be determined by passive elements in the network. The firing current is that current necessary to place the transistor or SCR in the conductive state when applied to the base or gate terminal. The holding current is that current which must pass between the two emitters of the two transistors configuration or between the anode and cathode of the silicon controlled rectifier in order to maintain the device in the conductive state. In firing amplifier 264 these currents are determined by the resistive network comprised of resistors 171, 172, 173, 174, and 17S. Additionally, an extra terminal, that is the collector terminal of transistor 170, is provided by the two-transistor configuration that is unavailable when a silicon controlled rectifier is used.

The aforementioned collector terminal of transistor -170 is supplied to a unijunction relaxation oscillator comprised of unijunction transistor 176, capacitor 177, resistor 178, resistor 179 and resistor 240. The rate of oscillation of this oscillator is determined by the various circuit components connected therewith and is designed to be much faster than the rate of pulse generation provided by unijunction transistor 168. It will be appreciated that, when a pulse is generated by unijunction transistor 168 triggering and retaining transistor 170 in the conductive state, a signal will be applied from the collector of transistor 170 to unijunction transistor 176 and a series of rapid pulses from the base terminals of unijunction transistor 176 will be supplied to pulse transformer 180 for the remainder of a synchronization period, hereinafter described. The pulses from unijunction transistor -176 are amplified by transistor 181 before being supplied to pulse transformer 180. Pulse transformer 180 is connected to two controlled rectifiers in armature controlled rectifier bridge 62 by output windings 380.

The rapid pulses from unijunction transistor 176 will be supplied to pulse transformer 180 for the remainder of the synchronization period determined by synchronizing circuit 182. Synchronizing circuit 182 includes transistor 183, rectifier 184, resistor 185, resistor 186, rectitier 187, and capacitor 188 and serves to synchronize the operation of firing amplifier 264 to the AC supply frequency. synchronizing circuit 182 is connected between the above described pulse generating components and a power supply comprised of transformer 189 and diodes and 192. The primary of transformer 189 is connected to alternating current supply lines 28.

At the beginning of `each positive half cycle of alternating current supplied by transformer 189, transistor 183 will be turned on rapidly by means of a signal supplied through rectifier 187 and resistor 185. Current flow through rectifier 187 also charges capacitor '188 so that its lower terminal is positive. The turning on of transistor 183 provides power to the remainder of firing amplifier 264 and allows a unijunction transistor 176 to generate rapid pulses to pulse amplifier 1'80 when transistor 170 has been turned on by unijunction transistor 168. The instant at which unijunction transistor 176 begins generating pulses is determined by the magnitude of the input signal to terminals 156 and 157, input signals of greater magnitude tending to initiate pulse generations earlier in the positive half cycle of alternating current power.

At the end of the positive half cycle of alternating current, capacitor 188 discharges through resistors -186- and 185. This provides a bias to the base of transistors 183 that allows that transistor to remain on for a portion of the negative half cycle. When capacitor 188 is discharged, transistor 183 becomes nonconductive, terminating pulse generation by unijunction transistor 176. The portion of the negative half cycle during which transistor 183 is conductive depends upon the magnitude of capacitor 188. Thus, firing amplifier 264 will initiate pulse generation by unijunction transistor 176 in the negative half cycle of alternating current power for a small input to terminals 156 and 157, ie., from time T3 to T4 in FIG. 2. As the input signal is increased, the initiation of pulse generation by unijunction transistor 176 will advance from the neagtive half cycle of alternating current power into the positive half cycle and may be moved to near the beginning of the positive half cycle of alternating current. The pulses generated by unijunction transistor 176 and supplied to pulse transformer 180 tend to place the controlled rectifiers in armature controlled rectifier bridge 62 in the conductive state. The controlled rectifiers will actually begin conducting when they have become properly biased across the anode and the cathode terminals.

By using a plurality of rapid pulses, armature controlled rectifier firing circuit 64 insures that the controlled rectifiers of armature controlled rectifier bridge 62 will be turned on at the earliest possible time they become properly biased across the anode and cathode. If the single pulse were employed to render the controlled rectifiers conductive, such pulse might be delivered at a time when the controlled rectifier was improperly biased and, hence, the controlled rectifier would never be turned on. The controlled rectifiers could also be turned on by AC rider or straight DC energization to the gate terminal. However, if signals of this type of'sufiicient magnitude to insure dependable firing are used, they cause excessive gate dissipation, shortening the life of the controlled rectifier. It will be appreciated that, with the plurality of rapid pulses of short duration provided by the armature controlled rectifier firing circuit 64, excessive gate dissipation is prevented yet reliable firing is provided, since each individual pulse may be of considerable magnitude. Additionally, as previously mentioned, armature controlled rectifier firing circuit 64 insures that the controlled rectifiers will be turned on as soon as they are properly biased across their anodes and cathodes.

Current regulating and regenerative logic circuit 66 supplies the control or input signal to armature controlled rectifier circuit 64. A circuit which may perform the functions of armature current regulation and regenerative logic is shown in FIG. V6. As its name implies, circuit 66 includes a regenerative logic portion 196 and a current regulating portion 197. Both the regenerative logic portion 196 and the current regulating portion 197 are energized by a power supply circuit consisting of transformer 217, rectifiers 218 and 219 and filter capacitors 220 and 221.

Regenerative logic portion 196 determines whether control is capable of regenerating or motoring on the basis of the polarities of the signals from operational amplifier 16 and from the motor field via conductors 68 and 69 and operates the armature circuit 20 accordingly. Regenerative logic portion 196 is comprised of two AND gates which require the correct combination of signal polarities from the aforesaid sources to produce an output from one of them.

More specifically, regenerative logic portion 196 is comprised of AND gate 1'98 and AND gate 199. AND gate 198 consists of transistor 200, connected in emitter follower configuration, and transistor 201, while AND gate 199 consists of transistor 202, also connected in emitter follower configuration, and transistor 203. The outputs of AND gates 198 and 199 are supplied through diodes 204 and 205, respectively, and through rheostat 207 to the input of current regulating portion 179.

The input signals to the regenerative logic AND gate 198 consist of the inverse output signal from operational amplifier 16 applied to input terminal 213 and the field polarity signal in conductor 68 applied to input terminal 214. The input signals to the regenerative logic AND gate 199 consist of the direct output signal from operational amplifier 16 applied to input terminal 21S and the field 18 polarity signal in conductor 69 applied to terminal input 216.

For either AND gate 198 or AND gate 199 to open and supply a signal to current regulating portion 197, input signals of the correct polarity must be present at both input terminals of the AND gate. For example, during motoring operation in one direction, an input signal from operational amplifier 16 is supplied to terminal 213 which is of a polarity to bias transistor 200 into the conductive state. An input signal from conductor 68 to terminal 214, indicating the direction of current ow in the motor field 26, will be of a polarity to bias transistor 201 off, thereby preventing that transistor from diverting the output of transistor 200 to conductor 227. This opens AND gate 198 and the output of transistor 200 which is proportional to the error signal in conductor 40, amplifier by operational amplifier 16, is supplied through resistor 304 and diode 204 to potentiometer 207 to control current regulating portion 197 which in turn controls the operation of armature firing circuit 64.

The polarity of the input signal from operational amplifier 16 to terminal 215 being of the opposite polarity of the signal applied to terminal 213 prevents transistor 202 from conducting and, hence, no signal can emanate from AND gate 199. Further, transistor 203 is biased on tending to divert any output from transistor 202 to conductor 227.

When control 10 undergoes regenerative operation, the polarities of the signals lfrom operational amplifier 16 to input terminals 213 and 215 reverse as the polarity of the error signal has reversed. This turns off transistor 200. The reversed polarity of the input signal to terminal 215, however, turns transistor 202 on. The polarity of the input signals to terminals 214 and 216 does not reverse instantaneously when control 10 initiates regenerative operation as it takes a finite time for the motor field 26 to reverse. During this time no signal will appear from AND gate 198 as transistor 200 is biased off and no signal will appear from AND gate 199 as transistor 203 diverts the output of transistor 202 since the polarity of the signal in conductor 69 applied to terminal 216 has not yet reversed.

When the direction of current flow through the motor field 26 does reverse, indicating the motor field is now ready for regenerative operation, the polarity of the signal in conductor 69 reverses. This turns off transistor 203 and opens AND gate 199 to provide a control signal through diode 205 to junction 206 which acts as a control signal during regenerative operation of the control.

Operation in the other direction of motor rotation is the opposite of the above described operation.

Current regulating portion 197 of current regulating and regenerative logic circuit 66 consists of a two stage amplifier with the associated input, feedback, and output circuits. The first of the amplifier consists of transistors 203 and 209 and is a differential stage. The total current through both transistors 208 and 209 is determined by the supply voltage across capacitor 221 and the value of resistor 222. A variation in the emitter collector current of transistor 208 provides an equal but opposite variation to the emitter collector current of transistor 209 in order to maintain the total current constant. This variation is applied to the base of transistor 210 forming the second stage of the amplifier. The output of the emitter collector circuit of transistor 210 is applied to output terminal 212.

The inputs to current regulating circuit 197 consist of the signal from the regenerative logic circuit 196 applied to potentiometer 207 and a signal proportional to armature current supplied to input terminal 211. The magnitude of the signal applied to junction 223 from regenerative logic circuit 196 is controlled by potentiometer 207 and the magnitude of the output signals of operational amplifier 16. This signal is then mixed with the current feedback signal at junction 223 to form an error signal which is supplied to the base of transistor 208. As the current feedback signal is a series of current pulses, the error signal is filtered through capacitor 230 and resistor 231.

A compensating feedback is also provided in current regulating portion 196. This is a negative feedback from the output of transistor 210 to the input of transistor 208 and is passed through capacitor 232 and resistor 233. This feedback alters the time response of the amplifier to prevent overshoot and to insure stable, balanced firing of armature controlled rectifier bridge 62. The compensating feedback must be of a sufficient magnitude so that there is no overshoot under the most severe input signal conditions.

The output signal is supplied to terminal 212. This output signal is inverted with respect to the input signal. Specifically, because of the differential configuration of transistors 208 and 209, an increase in the signal to the base of transistor 208 increases the output of that transistor While decreasing the output of transistor 209 since the total current flow through both of them must be constant. The decrease in output of transistor 209 is amplified by transistor 210 and supplied to output terminal 212. The reason for inverting the output signal is to simplify obtaining the negative feedback signal required for the compensating feedback. The polarity of the output from circuit 66 is arranged so that an increased error signal results in an increased or advanced firing angle to the controlled rectifiers in bridge 62.

The operation of the current regulating portion 197 of current regulating and regenerative circuit 66 is critical to the overall operation of control as portion 197 operates the previously described inner current regulating loop of the control. This inner loop is a true regulating circuit with both reference and feedback signals and is of high gain so that only a small error signal between the reference and the feedback is sufiicient to produce maximum output.

Because of the true regulating action of current regulation portion 197, the armature current is maintained at all times proportional to the reference signal from potentiometer 207, which is in turn proportional to the output signals of operational amplifier 16, except when the AND gates 198 and 199 of regenerative logic circuit 196 are not open.

Current limiting action of the inner current regulating loop occurs when the input signals to operational amplifier 16 are of sufficient magnitude to cause saturation of its output. When the output of operational amplifier 16 becomes saturated, a limit is reached in the magnitude of signal that can be delivered through either AND gate 198 or 199 and potentiometer 207. Since the signal through potentiometer 207 is the reference to current regulating portion 197, a limit is also placed on the amount of armature current that the inner current regulating loop will allow. This action provides the aforementioned sharp current limit. It will also be noted that the current limit action is obtained without the necessity of transiently excessive armature current to trigger the limiting means.

The compensating feedback through capacitor 232 and resistor 233 around current regulating portion 197 modifies its response to prevent overshoot of armature current under the most abrupt saturation of operational amplifier 16.

A full appreciation of the relationship and interaction of the detailed elements of the above described components in the structure and operation of the combination of the present invention may be had by referral to the foregoing description of operation of regenerative direct current motor braking control and reference is hereby made to that portion of the specification.

While the present embodiment of the invention is considered preferred, it is appreciated that numerous modifications may be made to the present invention. It is intended to cover in the appended claims, all such modificaf tions as wall within the true scopes and spirit of the invention.

20 I claim:

1. In combination, a static, regenerative direct current motor control which obtains regeneration of power from a motor operatively associated with the control to an alternating current power supply by reversing the motor field winding current; and a motor field circuit means coupled to the control and to the power supply and connectable to the motor field winding for providing current energization to the motor field winding from the power supply and for reversing through zero energization the direction of current flow through the motor field winding, said field circuit means having means for regeneratively discharging the inductive energy of the motor field winding to the power supply to rapidly decrease the field current to zero energization.

2. The combination of claim 1 wherein said field circuit means includes a controlled rectifier means connected to said alternating current power supply and responsive to half cycles of current therefrom for providing current flow in either direction through the motor field winding from the power supply, and a firing circuit for operating said controlled rectifier means in accordance with a bi-condition input signal from the control, said firing circuit operating said controlled rectifier means to provide current flow in one direction through the motor field winding when the input signal is in one condition and operating said controlled rectifier means to provide current flow in the other direction through the motor field winding when the input signal is in the other condition, said firing circuit including first signal means responsive to the presence and condition of said input signal for providing a first firing pulse to the controlled rectifier means during each half cycle of the alternating current power supply in accordance with the condition of said input signal for operating said controlled rectifier means to provide current fiow in a desired direction through the motor field winding, and said firing circuit also including second signal means for providing a second firing pulse to the controlled rectifier means during the half cycles of the alternating current power supply independently of said input signal, said second firing pulse being provided in the latter portions of the half cycles for regeneratively discharging the inductive energy of the motor field winding back to the power supply to rapidly decrease the field current to zero energization.

3. The combination of claim 2 wherein said firing circuit includes a pair of energizable pulse generating circuits coupled to said controlled rectifier means and said first signals means includes a differential amplifier connected to the pulse generating circuits for energizing the latter for providing first firing pulses from one pulse generating circuit in response to an input signal from one condition from said control for operating said controlled rectifier means to provide current fiow in one direction through the motor field from the power supply, said differential amplifier providing first firing pulses from the other of said pulse generating circuits in response to an input signal of the other condition for operating said controlled rectifier means to provide current fiow in the other direction through the motor field winding from the power supply, said second signal means being connected to said pulse generating circuits for energizing both said pulse generating circuits to produce said second pulses near the end of the half cycles of the alternating current power supply.

4. The combination of claim 1 wherein said field circuit means includes a resistor means therein for sensing the direction of current flow through the motor field winding and for providing a signal indicative of the direction of the current flow through the motor field winding.

5 In combination, a static, regenerative direct current motor control which obtains regeneration of power from a motor operatively associated with the control to an alternating current power supply by reversing the current through the motor field winding; and a motor field circuit means coupled to Said control and including two DC sources having their outputs connectable in parallel with the eld winding, said DC sources being responsive to a control signal from the control to the circuit means for providing a current flow through the motor field winding, the direction of the current flow provided by one of said DC sources being opposite the direction of the current flow provided by the other of said DC sources, said eld circuit means having a current limiting impedance inserted in the outputs of said DC sources, said DC sources including controlled rectiers interposed between said alternating current power supply and the motor field winding for selecting the direction of current flow and for rectifying half cycles of the alternating current to provide the current ow, one of said DC sources having at least one of said controlled rectiers poled to conduct current in one direction through the motor ield winding, the other of said DC sources having at least another of said controlled rectifiers poled to conduct current in the other direction through the motor eld winding, said controlled rectifiers being placed in the nonconductive state by alternate half cycles of alternating current, so that in the event the controlled rectiers in both DC sources simultaneously provide current, said condition may exist for only one half cycle of the alternating current, and said impedance limits the current through the DC sources, thereby to prevent damage to the DC sources.

6. The combination of claim 5 wherein said DC sources include controlled rectiiiers interposed between said alternating current power supply and the motor field winding for selecting the direction of current ow and for rectifying half cycles of both polarities to provide the current iiow, one of said DC sources having a pair of controlled rectiers poled to conduct current in one direction through the motor eld winding when in the conductive state, the other of said DC sources having a pair of controlled rectiers poled to conduct current in the other direction through the motor field winding when in the conductive state, the controlled rectiiiers of each pair being alternately placed in the nonconductive state by the half cycles of alternating current, so that in the event controlled rectitiers in both DC sources simultaneously provide current, said condition may exist for only one half cycle of the alternating current.

7. The combination of claim S wherein said eld circuit means includes a resistor means interposed between the outputs of said DC sources and the motor eld winding for sensing the direction of current ow through the motor eld and for providing a signal indicative of the direction of the current ow through the motor field winding.

8. The combination of claim 7 wherein said controllable DC sources include means for regeneratively discharging the inductive energy of the motor eld winding to the power supply of said sources to rapidly decrease the eld current to zero.

References Cited UNITED STATES PATENTS 3,284,689 11/1966 Rosa S18-345 X 3,421,065 l/l969 Stabile 3l8-338 X ORIS L. RADER, Primary Examiner R. J. HICKEY, Assistant Examiner U.S. Cl. XR, 31E-338, 492. 

